Holland
braking system



Aug. 12, 1989 H. c. HOLLAND BRAKING SYSTEM Original Filed Feb.

5 Sheets-Sheet 1 FIG. I

INVENTOR. HARVKSON C. HOLLAND AT TQRNEY BRAKING SYSTEM 5 Sheets-Sheet. 2

Original Filed Feb. 15, 1965 D a v m Y D T m m 5 mm w V A h m C. 4 N wG. 0 n w M H. Q m M w v H 5 [MW 5:: L 5:; i, E p M...

FIG.2

ATTORNEY Aug. 12, 1969 H. c. HOLLAND Re. 26,643

BRAKING SYSTEM Original Filed Feb. 15, 1965 5 Sheets-Sheet 3 TOTALSTOPPING FORCE INVENTOR. HARVISON c HOLLAND BY 6 ATTORNEY H. C. HOLLANDBRAKING SYSTEM Aug.- 12, 1969 5 Sheets-Sheet 4 Original Filed Feb. 15,1965 INVENTOR.

HARVISON C4 HOLLAND ATTORNEYS Aug. 12, 1969 H. c. HOLLAND 25,543

BRAKING SYSTEM Original Filed Feb. 15. 1965 5 Sheets-Sheet 5 IO G) FIG.9

1N VENTOR.

HARVISON C. HOLLAND Y B (42L ATTORNEYS United States Patent Int. Cl.B60t 8/02 11.8. CI. 303-6 17 Claims Matter enclosed in heavy bracketsappears in the original patent but forms no part of this reissuespecification; matter printed in italics indicates the additions made byreissue.

ABSTRACT OF THE DISCLOSURE A braking arrangement including two hydraulicsystems, one for the front wheels and the other for the rear wheels,each system having a master cylinder arranged so that upon movement ofthe actuator the piston in the system for the front wheels acceleratesrelative to the piston for the system for the rear wheels so that theratio of the stopping force at the front wheels to that at the rearwheels increases with increased braking effort, the systems producingsufiicient movement of the pistons to take into account the relaticestiflnesses of the two systems so that stopping forces are produced atthe front and rear wheels to provide maximum braking efiort withoutskidding.

This application is a continuation-in-part of my copending applicationSerial No. 225,526, filed September 24, 1962, for Braking System, nowabandoned.

This invention pertains to the brakes of a vehicle and o particularly toa means for properly distributing the brakink forces to achieve maximumeffectiveness.

In the stopping of a vehicle such as an automobile, truck or the like, agreater amount of decelerating force can be applied at the front Wheelsthan at the rear. The center of gravity of the vehicle is located aboveand to the rear of the axes of the front wheels. When the vehicle isdecelerated by applying the brakes, a force couple is produced thatreacts downwardly on the front wheels as well as forwardly. Hence, thefront wheels are pressed more tightly against the surface of the road asthe vehicle is slowed. This also reduces vertical load on the rearwheels during deceleration. The faster the stop the greater thedeceleration and the more pronounced is the effect. This means that thefront wheels, with their greater downward load, have less tendency toslide than do the rear wheels where the load is reduced as the vehicleslows down. As a result, when the brake pedal is pushed for a rapidstop, the rear wheels will be caused to skid at a point considerablybefore a maximum braking force has been achieved at the front wheels.The lighter effective weight at the rear of the vehicle allows the rearwheels to commence a slide under such conditions. As soon as theskidding of the rear wheels is encountered, a major portion of theirbraking effectiveness is lost. The reduced coefficient of slidingfriction of the tires of the rear wheels will offer far less resistingforce than the higher coefficient of static friction that governs priorto the inception of the skid. Hence, the effect of the deceleratingforces on the vehicle is to cause a loss of braking ability as the rearwheels slide while the front wheels continue to rotate. In addition, thesliding of the rear wheels will make the vehicle more diflicult toc0ntrol and can cause the vehicle to yaw or spin around.

In an effort to improve vehicle brakes it has become a frequent practiceto provide larger wheel cylinders and ice more brake shoe lining area atthe front wheels than at the rear. However, while this improves brakingperformance to a degree, it provides an optimum ratio of front to rearbraking effort for only one coefficient of friction between the tiresand the road. In practice this works out to be approximately thatcoefficient produced by wet streets. The result is that the rear wheelsslide when the front wheels have developed only a portion of theirmaximum braking effort on dry paving and the front wheels slide when therear wheels have developed only a portion of their maximum brakingeffort on snow or ice. In the latter case, ability to steer the vehicleis lost.

Furthermore, it results in excessive front end ducking of the vehicle,as well as concentrating the wear of the brakes at the front wheels fornormal light to moderate braking forces. More brake adjustments becomenecessary also because of the unequally distributed brake loads.

The arrangement of this invention provides a simplitied means by whichthe front brakes are made to exert a force that increases more rapidlythan the force at the rear brake as the brake pedal is advanced. Inother words, the more rapid the stop the higher the proportion of thestopping forces concentrated at the front wheels. This inventionproperly balances the braking forces between front and rear so thatthere will be no more tendency to slide at the back than at the frontunder all road conditions, wet or dry, slippery or not. This permits amaximum stopping force to be realized under all road conditions, whileobviating the disadvantages noted above for other systems.

This is accomplished through the provision of a dual master cylinder,one cylinder of which serves the two front brake cylinders, while theother is for the rear brakes. The linkage connected to the brake pedalcauses the piston in the front master cylinder to accelerate relative tothe piston in the master cylinder for the rear system as the brake pedalis depressed. This may be accomplished through the use of two crank armspositioned to impart differential movement to the pistons.Alternatively, cams may be used to accomplish this result. When crankarms are utilized, gears preferably are included to increase the crankarm rotation relative to that of the brake pedal.

This relatively simple [leakage] causes the front brakes to exert anincreasingly greater stopping force as the pedal is pressed inwardly.The system of this invention also assures that the brakes at the frontand rear initially come into operation simultaneously, applying thegreater braking force at the front only after this has beenaccomplished. This may result from an appropriately positioned portbetween the two master cylinders, closed off after one of the pistonshas beenmoved a predetermined distance. Alternatively, in order tocompensate for wear in the braking system, an automatically operablevalve may disconnect to the two hydraulic systems only after an initialbraking force has been encountered at both the front and rear of thevehicle.

It is an object of this invention to provide an improved braking systemfor vehicles.

Another object of this invention is to provide a vehicle braking systemenabling the vehicle to stop in a minimum distance by appropriatedistribution of braking forces.

A further object of this invention is to provide a braking system inwhich all of the wheels will exert a maximum braking force before anywill start to slide.

An additional object of this invention is to provide an improved brakingsystem usable with virtually any type of vehicle brakes.

Yet another object of this invention is to provide a braking systemwhich distributes the force from a single pedal among the brakes at thewheels in proportion to the maximum total stopping force that the wheelscan exert under all conditions.

These and other objects will become apparent from the following detaileddescription taken in connection with the accompanying drawing in which:

FIGURE 1 is a longitudinal sectional view illustrating the brakingsystem of this invention;

FIGURE 2 is a schematic view showing the overall arrangement of thesystem as associated with a vehicle;

FIGURE 3 is a graph illustrating the braking effect achieved by theprovisions of this invention compared with other braking arrangements;

FIGURE 4 is a sectional view showing a means for preventing independentoperation of the front and rear brakes prior to the engagement of thebrakes both front and rear;

FIGURE 5 is a plan view of a different embodiment of the actuatingmechanism in which gears are included to impart greater rotation to thecrank arms;

FIGURE 6 is a longitudinal side elevational view, partially in section,taken along line 6-6 of FIGURE 5',

FIGURE 7 is a schematic view of the kinematics of the actuating crankarms;

FIGURE 8 is a plan view of an embodiment accomplishing the differentialpiston movement by the use of cams;

FIGURE 9 is a longitudinal section view taken along line 99 of FIGURE 8;and

FIGURE 10 is a transverse sectional view taken along line 10-10 ofFIGURE 9.

With reference to FIGURE 1 of the drawing, the braking system of thisinvention includes a master cylinder assembly 1 made up of a duality ofbraking cylinders 2 and 3 arranged with their axes parallel. Thesecylinders may be of the same diameter and interiorly may be generallyconventional insofar as their basic components are concerned. Hence.within the cylinders there are reciprocative pistons 4 and 5 that ontheir forward ends carry flexible cups 6 and 7 that seal against thecylinder walls. Hydraulic fluid is contained in reservoir 8 and enterscylinder 2 on both sides of the piston 4 through the ports 9 and 10.Additional ports 11 and 12 connect the fluid supply source to the othercylinder 3. The pistons 4 and 5 include rearward extensions 13 and 14that at their distal ends carry sealing elements 15 and 16. On theirother sides the pistons 4 and 5 are engaged by compression returnsprings 17 and 18 that extend to the opposite end walls 19 and 20 of thecylinders. These springs bias the pistons to their retracted positionsillustrated where they engage stops 21 and 22. Two-way check valveassemblies 23 and 24 are included in the normal manner at the cylinderoutlets. Lines 25 and 26 connect to the ends 19 and 20 of the cylinders2 and 3 for conducting the hydraulic fluid to the wheel cylinders. Asshown schematically in FIGURE 2, line 25 leads to the brakes 27 and 28at the front wheels, while the line 26 connects to the rear wheel brakes29 and 30. The brakes at the wheels may include conventional shoes anddrums, or may be disc or other types of brakes. The system of thisinvention can be used with almost any kind of brakes at the wheels.

The brake pedal 31 includes an arm 32 that is pivotal about the axis ofa shaft 33 which may be supported by the chassis of the vehicle. Thisshaft is spaced from the ends of the cylinders with its axis in a planeperpendicular to the plane of the axes of the cylinders. A bell crank 35likewise is mounted on shaft 33 and is Coupled to rotate with the arm32. Therefore, when the pedal 31 is pushed downwardly, the bell crank 35is caused to rotate about the axis of shaft 33 as a result of themovement of arm 32. This movement is clockwise as the invention isillustrated in FIGURE 1.

The bell crank 35 includes a relatively long arm 36 that by means ofpivot pin 37 connects to a rod 38. The latter member extends throughflexible rubber dust cover 39 into the end of the cylinder 2 of thefront wheel system. There it engages the piston 4 so that the pistonwill be caused to move with the rod 38.

A shorter arm 40 of the bell crank connects by pin 41 to push rod 42which extends into cylinder 3 for actuating the piston 5.

It can be seen, therefore, that when the brake pedal is pushed and thearm 32 rotated clockwise, the bell crank 35 is rotated toward thecylinders and causes the push rods 38 and 42 to move to the right. This,in turn, advances the two pistons 4 and 5 in the cylinders. After arelatively short travel of the piston 4, port 10 will be passed and thehydraulic fluid for both front and rear brakes in lines 25 and 26becomes pressurized. Immediately thertafter, pistons 4 and 5 both passport 12, cutting off communication between the cylinders 2 and 3 aheadof the pistons. Consequently, the front brake system, serviced throughline 25, is separated and operated independently of the rear brakesystem receiving fluid from line 26 of the other cylinder 3.

This construction results in the application of a braking force at thefront cylinders which increases more rapidly than that at the rearcylinders as the brake pedal is advanced through its travel. This isbecause the bell crank 35 gives more lineal movement to the rod 38 thanit does to the rod 42. Arm 36 is longer than arm 40 of the bell crank,which means that a longer are will be described at pivot pin 37 than atpin 41 as the bell crank rotates. The axis of cylinder 2 for the frontwheels is spaced farther away from pivot shaft 33 than the axis of theother cylinder 3. Hence, rod 38 travels substantially tangential to thearc traversed by pin 37, and most of the arcuate distance is convertedinto a relatively large amount of rectilinear movement of piston 4.

Also, the arm 36 is located to the left of an imaginary line 43 which isnormal to a projection of the axes of the cylinders 2 and 3 and extendsfrom the pivot shaft 33. Bell crank arm 40, on the other hand, ispositioned to the right of this line. The significance of this is thatas the arm 36 rotates clockwise it imparts an ever-increasing proportionof movement along the line of the axis of. cylinder 2, because it isapproaching the line 43 perpendicular to that axis. At the same time,arm 40 moves away from the line 43 and thereby produces a continuallydecreasing amount of movement in the direction of the axis of cylinder 3to the push rod 42. The result is that piston 4 moves farther and at anincreasing rate as it approaches the outlet end of the cylinder. Piston5 moves a lesser distance and decreases in its rate of movement as theend of the cylinder is neared. This means that the force applied at thefront brakes becomes higher proportionately to that of the rear brakesas the brake pedal is advanced. This is precisely the effect needed inobtaining optimum stopping of the vehicle.

In this manner it is possible to obtain almost exactly the type ofbraking forces needed, thereby greatly increasing the ability of thebrake system to stop the vehicle. It may be observed that the systemoperates on the linkage and master cylinders of the brake system, andhence is independent of the precise form of brakes that are used at thewheels. The important thing is that this system distributes the brakingforces properly for all conditions giving a maximum stopping force forrapid deceleration while not overloading the front brakes during moregentle stops.

The significance of the changing application of braking force front andrear may be observed from the graph of FIGURE 3. Here the abscissarepresents the total braking force on the vehicle, while the ordinate isthe ratio of stopping force at the front wheels to that at the rear. Thecurves are for conditions where the tires of the vehicle do not slide onthe road surface. Curve A depicts the effect of a conventional brakingsystem. The proportion of stopping force front to rear does not varywith the total force applied to stop the car no matter how great therate of deceleration. Hence, curve A is merely a straight horizontalline. If the front brakes are made to lead the rear brakes, applying theshoes to the front drums before engagement at the rear, the results willfollow curve B. It can be seen that for low stopping forces a muchgreater proportion is borne by the front brakes, but that the ratiodecreases as stopping force becomes larger. Hence, instead of the frontbrakes absorbing a greater share of the braking load as their ability toresist rotation without skidding the front wheels becomes larger, theopposite is true and the curve drops off to the right.

It can be demonstrated both mathematically and empirically that curve Crepresents ideal conditions for deceleration. As indicated, the ratio offront to rear stopping force becomes larger with increased total brakingforce. Thus, the curve inclines upwardly to the right. The brakingsystem of this invention provides a very close approximation of curve C,increasing the ratio in substantially the same manner.

The aperture 12 interconnecting the cylinders 2 and 3 does more thanassure that both cylinders are released and equalized at the beginningof the braking stroke of the pistons. It also prevents the brakes at thefront from being applied to the brake drums prior to the engagement ofthe rear brakes. It would be a safety hazard if the front brakes cameinto actuation before the rear brakes and also would lead to excessivewear at the front, loss of adjustment, and nosing down on light brakeapplications. Therefore, by positioning the aperture 12 axially inwardof the piston 5 in the retracted position, the brake systems for thefront and rear wheels are interconnected and act together for theinitial portion of the movement of the brake pedal. It is only after thepiston 5 reaches the aperture 12 that the two systems are separated andbecome independent. The simple provision of the aperture 12 at aposition spaced a predetermined distance from piston 5, therefore,normally assures that the brakes will operate together and thatundesirable effects will not be encountered through the use of thesystem of this invention.

However, the aperture 12 is a suflicient means for separating thehydraulic actuation of the front and the rear brakes to produce theforegoing described #results only when wheel brake mechanism adjustmentis such that the shoes contact the drums at the same time that piston 5closes aperture 12. This condition can be expected to hold over a longperiod of time when the Wheel brakes include self-adjusting features.Otherwise, when the brakes have worn, aperture 12 will close before thebrake shoes have contacted the drums, which will cause the front brakesto lead the rear brakes. This will result in performance similar to thatindicated by curve B of FIGURE 3.

In order to prevent any such occurrence, the arrangement shown in FIGURE4 may be provided in connection with the system of this invention. Thisincludes a valve unit 44 located in a bypass line 45 between the line 25to the front brakes and the line 26 to the rear brakes.

Valve unit 44 includes a central chamber 47 having a valve seat 48 whichmay be engaged by an axially movable valve element 49. A stem 50 extendsfrom the member 49 through a wall 51 to a chamber 52. Within the chamber52 is a reciprocative piston 53 connected to the end of stem 50. Acompression spring 54 is interposed between the end wall 55 of thecylinder 52 and the face of the piston 53. A vent opening 56 is providedin wall 55 which is covered over by a dust boot 57. The latter elementalso includes a vent opening 58.

In operation of the arrangement of FIGURE 4, upon initial movement ofthe brake pedal there will be free communication of fluid through thebypass line 45, permitting circulation through the open valve unit 44.This is because the spring 54 biases the piston 53 and hence the valvemember 49 to the left, as illustrated, away from the valve seat 48.Until such time as both sets of brakes are engaged, the bypass willmerely transmit fluid, and pressure will not develop at the valve. Assoon as the brakes are in engagement both front and rear, however, therewill be a resisting force built up in both line 25 and line 26. Thiscauses a back pressure in the bypass line 45 and also in the valvechamber 47. The fluid in the valve is free to pass through openings 59in the wall 51 between chamber 47 and the cylinder 52. This pressurethen reacts against the face of piston 53 overcoming the resisting forceof spring 54. Thus, the fluid in the hydraulic lines from the brakecylinders reacts against the piston to move the piston to the right.Thus, through stem 50, causes the valve member 44 to contact the seat48. As a result, the bypass 45 is closed and the two brake systems areseparated.

Therefore, the valve element 44 assures that when both the front andrear brakes are in engagement the two systems are cut off from eachother and can operate independently in the intended manner. Since thevalve unit 44 operates on the basis of a resisting force from both thefront and rear brakes it will not close off the bypass until the brakeshoes are in engagement at both sets of wheels. Brake adjustment has noeffect on the valve unit 44. Accordingly, in some instances it isdesired to utilize the valve arrangement between the two brake systemsto assure that the arrangement of this invention will always operatesatisfactorily.

In order to preserve the proper relationship of the angular movement forthe crank arms used in actuating the pistons in the front and rearsystems, while at the same time utilizing a normal increment of travelfor the brake pedal, it is necessary in many vehicles to provide anincrease in the rotation of the crank arms that drive the pistons overthe rotation of the arm of the brake pedal. As pointed out above, it isimportant to assure that the piston in the cylinder for the front systemaccelerates at a controlled rate relative to the piston for the rearsystem at the time these systems are separated and the brake shoesengage the drums. If optimum braking is to be realized, the distancestraveled and the rates of movement of the pistons in the mastercylinders for the two systems must be in accordance with exact values.In accomplishing this, their crank arms should be of predeterminedlengths and rotate through established arcs, carefully located withrespect to the center lines of the cylinders. By this arrangement, onecrank arm approaches the vertical with respect to the cylinder axes,while the other crank arm moves away from the vertical line.Nevertheless, with the driver in a seated position while applying thebrakes, the movement of the foot in pressing on the brake pedal islimited. If the brake application requires to long an increment oftravel of the brake pedal, the operator of the vehicle will have greatdifliculty in moving the brake pedal a sufiicient distance. This isparticularly true in view of the habits motorists have acquired inoperating brakes of conventional design.

In correlating the appropriate amount of brake pedal movement with thatof the crank arm, gearing may be included in the operating mechanism asillustrated in the embodiments of FIGURES 5 and 6. This allows the crankarms to be relatively short and to travel through larger arcs than thearc traversed by the brake pedal. This arrangement illustrates the brakecylinders mounted side by side rather than one above the other as in theversion of FIGURES 1 through 4. The positioning of the cylinders in thisregard is optional.

As shown in FIGURES 5 and 6, the brake pedal arm 60 is rotatable in acounterclockwise direction about its mounting pin 61 as the pedal isdepressed to apply the brakes. A bifurcated bracket 62 is used torotatably support the pin 61. Also mounted on the pin 61 and connectedto the pedal arm 60 is a gear sector 63 which moves with the brake pedalarm 60 and through an identical arc to that described by the brake pedalarm as the brakes are applied.

Meshing with the sector 63 is a second gear sector 65, rotatable about ashaft 66. A suitable bearing support, such as the bearing 67 shown inFIGURE 5, is used to mount the shaft 66 on the vehicle. The radiusbetween the center line of the shaft 66 and the pitch line of the teethof the sector 65 is less than the radius between the center line of pin61 and the pitch line of the teeth of the sector 63. Hence, the effectis that of driving a smaller gear by a larger one so that the rotationof the sector 63 produces a larger arc of rotation of the sector 65. Theamount of arc amplification achieved in this manner will depend upon theindividual system involved. In a typical example, a six to one gearratio is used.

Rotating with the shaft 66 are crank arms 69 and 70. The former is usedto drive the piston in the cylinder connected to the front brakes, whilethe latter actuates the piston for the rear brakes. A pin 71 at theouter end of the crank arm 69 connects this arm to a push rod 72. Thelatter element, through pin 73, is connected to piston rod 74 which ismovable axially in a bearing 75 at the outer end of the master cylinderfor the front system. Therefore, when the sector 65 is rotated in aclockwise direction by counterclockwise rotation of the sector 63,rectilinear movement is imparted to the piston rod 74 through the pushrod 72. The rod 74 at its inner end (not shown) connects with the pistonfor the front master cylinder, thereby displacing the fluid in the frontmaster cylinder in the manner previously described.

Similarly, the rotation given the drive crank arm 70 is transmittedthrough a connecting pin 76 to a push rod 77. The opposite end of therod 77 is joined by a pivot pin 78 to a piston rod 79 which extends intothe cylinder for the rear brake system and is axially slidable in ahearing 80. Consequently, the pistons in both master cylinders are movedthrough their strokes by the action of the brake pedal, although thedrive arms for the systems are moved through a greater are than is thebrake pedal.

With reference to the schematic illustration of FIG- URE 7, it may beseen that in the power stroke the crank arm 69 for the front systemapproaches the vertical line 81 that is normal to the axes of the twomaster cylinders. At the same time, the crank arm 70 recedes from thevertical line 81. Consequently, at the time when the front and rearsystems are separated, the piston in the front cylinder will be causedto accelerate relative to the piston in the rear master cylinder. Thisenables the results shown graphically by the curve C in FIGURE 3 to beobtained. As before, the braking effort at the front wheels will becontinuaily increased over that at the rear as the brake pedal isdepressed further. Therefore, the brakes at the front of the vehiclewill be called upon to exert an increasing amount of decelerating forceproportionate to that of the brakes at the rear of the vehicle as thetotal stopping force becomes greater.

The mechanism utilized with this invention is designed to take intoaccount an unapparent characteristic of flexibility that exists in anyhydraulic system. While commonly thought of as incompressible, thehydraulic fluid actually becomes compressed a small amount when thebraking force is applied to it. This decrease in fiuid volume underpressure plus the elasticity of the steel lines, cylinders and shoes, aswell as that of the rubber hoses, sealing caps, asbestos linings, etc.,that make up the hydraulic circuit, result in an elastic characteristicof the complete system. This elastic characteristic of the system issometimes referred to as its stiffness. The elasticity is responsiblefor the travel of the brake pedal or other part used in producing apressure change in the hydraulic system as the brakes are applied. Thus,as the braking force is increased, the brake pedal will continue to moveeven though there is contact between the brake shoes and the drumbecause of the elasticity in the system.

By separating the hydraulic system for the front wheels from that forthe rear and compressing the front wheel system at an accelerating ratewith respect to the rear wheel system, it is possible to produce brakingforces at the front and rear wheels corresponding to those ideallyrequired. In other words, the curve of available braking force in thismanner can be made to match the ideal curve of required braking forceindicated by the curve C in FIGURE 3. The curve of ideal requiredbraking force, in turn, is calculated from the relationship between thecenter of gravity of the vehicle and the contact points of the tires tothe road at various coeflicients of friction between the tires and theroad. Hence, the ideal curve of required braking force is a function ofthe geometry of the vehicle. The actual braking force available is madeto follow the ideal curve by properly relating the motion of the pistonsin the front and rear system master cylinders. In establishing thepiston movements required to permit the ideal curve C of FIGURE 3 to befollowed, it is necessary to make allowance for the stiffnesses of thefront and rear systems, as well as the relative sizes of the front andrear wheel systems and the front and rear system master cylinders.

It may be noted that the crank arm 70 for the rear system is slightlylonger than the crank arm 69 for actuating the front brakes.Nevertheless, the acceleration of the piston in the front systemrelative to the piston for the rear system will take place during thetime when the two systems are separated (the last third of the travel ofthe crank arms). This results from the fact that the crank for the frontsystem 69 is approaching the perpendicular line 81, whereas the crankfor the rear system is approaching a point from this line. Thetrigonometric relationships controlling such motion are apparent fromFIGURE 7. The stiffnesses of the front and the rear systems, as Well asthe sizes of the wheel cylinders, the master cylinders, the anglebetween the crank arms and the angle of the crank arms when the systemsare separated, will determine the length of each crank arm. Thus, eachparticular vehicle configuration will determine its appropriate crankarm length.

The embodiment of FIGURES 5 and 6, therefore, accomplishes basically thesame objectives of the previously described arrangement, but assuresthat the brake pedal can be moved through a normal amount of travel inapplying the brakes. Nevertheless, the gearing between the brake pedaland the crank arms is a relatively simple device that is economical toconstruct and incorporate in the mecahnism.

As an added feature to assure correct application of the front and rearbrakes, the effective lengths of the push rods 72 and 77 are adjustable,this being accomplished by providing eccentrics in the bolts 73 and 78.Thus, as shown for bolt 73, the threaded shank 82 is offset from and ofsmaller diameter than the portion 83 that fits through the push rod 72.The bolt 73 may be rotationally positioned to establish its effectivelength at a desired value with respect to the piston and the crank arm69, at which time the nut is tightened to clamp the bolt shoulder 84against the side of the piston rod 74. When the mechanism is actuated,the rod 72 rotates around the portion 83 of the bolt 73. The bolt 78 isconstructed in a similar manner.

This adjustment allows the linkage to be set so that the front and rearhydraulic systems become separated at the time when the crank arms areat their correct rotational positions to subsequently generate therequired strokes and differential displacement of the pistons. Inutilizing the valve 44 of FIGURE 4, the front and rear systems havebecome separated upon generation of a predetermined back pressure, asdescribed above. This back pressure can be created only when the portsor valves on the forward sides of the pistons in the master cylindersare closed to shut off communication with the reservoir. In other words,a back pressure can be generated only when the port 10 is closed in thedesign shown in FIGURE 1, so that fluid is not merely circulated to thereservoir and the back sides of the pistons as the pistons move. Theadjustment in effective lengths of the push rods 72 and 77, as affordedby the eccentric connecting bolts 73 and 78, allows the pistons to beadjusted properly relative to the reservoir shutoff ports to result inthe generation of the critical back pressure at the proper rotationalpositions of the crank arms 69 and 70.

Another means for causing the appropriate movement of the two pistons inthe master cylinder with the acceleration of one piston relative to theother is accomplished by the arrangement shown in FIGURES 8, 9 and 10.Here, the brake pedal 85 turns the transverse shaft 86 which isrotatably supported at the ends of brackets 87 and 88. This shaft pivotswith it a sleeve 89, from which extends a pair of spaced cam members 90and 91. The cam 90 has a curved actuating surface 92 of a predeterminedprofile, which is engaged by a follower roller 93, rotatably mounted bypin 94 on a piston rod 95. This is the piston rod for the mastercylinder 96 for the front brake system. The piston rod 95 slides axiallyin a bearing 97, and is prevented from rotation by being slotted on itsunderside, providing an axial recess into which fits the end 98 of ascrew 99.

A cam follower 100 bears against the curved profile 101 of the other cam91. The follower 100 is mounted by pin 102 on the end of piston rod 103.The latter member is the piston rod for the rear brake system, extendingthrough a sleeve bearing 104 into the rear master cylinder 105. The end106 of a screw 107 fits in an axial slot in the rod 103 to preventrotation of the rod.

It may be observed that the profile surfaces 92 and 101 of the two camsare the same adjacent their followers when the brakes are in theretracted positions shown in FIGURES 8 and 9. However, the surface 101curves inwardly with respect to the surface 92 at the power portions ofthese surfaces. When the cams are rotated in a counterclockwisedirection as viewed in FIGURE 9 by rotation of the shaft 86 by the brakepedal, they move the piston rods 95 and 103 rectilinearly to the right,as illustrated, thereby driving the pistons in the master cylindersthrough their strokes in applying the brakes. At first, the pistons willmove together because the cam surfaces are alike where the followers areengaged. However, when the lower portions of the profiles 92 and 101 arereached, the rod 95 for the front system will accelerate relative to therod 103 for the rear system. Hence, the piston in the front mastercylinder will accelerate relative to the piston in the rear mastercylinder as these portions of the cams are brought into play.

Again, therefore, the necessary acceleration of one piston relative tothe other is achieved. The two pistons are moved together for theinitial increment of their travel because this is the distance whichmust be moved in bringing the brake shoes into contact with the brakedrums. However, after the brake drums have been contacted, the requiredamount of acceleration of the front piston relative to the rear takesplace. Consequently, the effect insofar as the front and rear brakes areconcerned is the same as described above with the mechanism utilizingcams rather than crank. arms to bring about the differential movement.

The rotational positions of the cams 90 and 91 are adjustable relativeto the cam followers 93 and 100 for the same reasons that the effectivelengths of the push rods 72 and 77 of the embodiment of FIGURES and 6are adjustable. This is to assure that the proper portions of the camprofile are contacted by the followers when the back pressure builds upto a value sufficient to close the valve 44.

The cam adjustment is accomplished by providing an eccentric portion onthe shaft 86. The central portion 108 of the shaft 86, which passesthrough the cam sleeve 89 is offcenter with respect to the ends 109 and110 of the shaft. Therefore, when the nut 111 is loosened, the shaft 86may be rotated to vary the positions of the cam profiles 92 and 101 withrespect to the followers 93 and 10 100. Then the nut 111 is tightened toretain the adjustment.

From the foregoing description it can be seen that I have provided animproved braking system assuring an optimum stopping effect by properlybalancing the forces at the front and rear wheels of the vehicle. Nolonger will it be characteristic of the brakes to slide at the rearduring rapid deceleration. Also, there is no disproportionally highbraking force at the front during light braking conditions. Despite theimproved braking effort afforded by the teachings of this invention, theconstruction is relatively simple and can be accomplished at a low cost.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit arid scope of thisinvention being limited solely by the appended claims.

I claim:

1. In combination with a vehicle, a braking arrangement for said vehiclecomprising front wheel brakes, rear wheel brakes,

a duality of hydraulic systems, each of said systems including a masterhydraulic cylinder,

the first of said systems being connected to said front wheel brakes,

and the second of said systems being connected to said rear wheelbrakes,

a first piston in said first cylinder,

a second piston in said second cylinder each of said pistons beingmovable through a stroke for forcing hydraulic fluid to the brakes atthe wheels,

actuating means for said pistons, said actuating means including a firstpivotal arm connected to said first piston for determining the movementof said first piston through its stroke,

a second pivotal arm connected to said second piston for determining themovement of said second piston through its stroke,

and means for simultaneously rotating said pivotal arms through equalarcs,

said pivotal arms being positioned such that said first pivotal armestablishes movement of said first piston at a rate accelerated withrespect to the movement imparted to said second piston during at least asubstantial portion of said strokes of said pistons, and means forinterconnecting said system during initial portions of said strokesuntil both said front wheel brakes and said rear wheel brakes areapplied, and for separating said systems following such application ofsaid brakes during the remainder of said strokes.

2. In combination with a vehicle having hydraulic brakes at the frontwheels thereof and at the rear wheels thereof, a braking systemcomprising a duality of hydraulic systems, each of said systemsincluding a master hydraulic cylinder,

the first of said systems being operatively connected to said brakes atthe front wheels, the second of said systems being operatively connectedto said brakes at the rear wheels,

a piston in each of said cylinders for forcing fluid therefrom in thesystem thereof in a pressure stroke of such piston from a retracted toan extended position,

a brake pedal,

mtilanls rotatably mounting said brake pedal on said vemeansinterconnecting said brake pedal and said pistons for translatingrotation of said brake pedal into rectilinear movement of said pistonsthrough said strokes,

said translating means including means for causing said piston in saidfirst cylinder to accelerate relative to said piston in said secondcylinder during at least a substantial portion of said strokes of saidpistons,

and means for interconnecting said systems during initial portions ofsaid pressure strokes until substantially the point of application ofsaid brakes at said front wheels and at said rear Wheels and forseparating said systems following such application of said brakes.

3. In combination with a vehicle having hydrauilic brakes at the frontwheels thereof and at the rear wheels thereof, a braking systemcomprising a duality of hydraulic systems, each of said systemsincluding a master hydraulic cylinder,

the first of said systems being operatively connected to said brakes atthe front wheels, the second of said systems being operatively connectedto said brakes at the rear wheels,

a piston in each of said cylinders for forcing fluid therefrom in thesystem thereof in a pressure stroke of such piston from a retracted toan extended position,

a brake pedal,

means rotatably mounting said brake pedal on said vehicle,

a duality of crank arms,

said crank arms being operatively connected with said pistons forimparting rectilinear movement to said pistons upon rotation of saidcrank arms to drive said pistons through said strokes,

said crank arms being positioned such that the crank arms connected tothe piston for said first cylinder imparts rectilinear movement theretoat an accelerating rate with respect to the rectilinear movementimparted to said piston in said second cylinder,

means interconnecting said brake pedal and said crank arms for causingsaid crank arms to rotate simultaneously with said brake pedal and torotate through a larger arc than that of said brake pedal,

and means for interconnecting said systems during initial portions ofsaid pressure strokes substantially until the time of application of thebrakes at said front wheels and at said rear wheels and for separatingsaid systems following such application of said brakes.

4. In combination with a vehicle having hydraulic brakes at the frontwheels thereof and at the rear wheels thereof, a braking systemcomprising a duality of axially parallel master hydraulic cylinders,

the first of said cylinders being operatively connected to said brakesat the front wheels,

the second of said cylinders being operatively connected to said brakesat the rear wheels,

a piston in each of said cylinders for forcing fluid therefrom in apressure stroke from a retracted to an extended position,

a brake pedal,

means rotatably mounting said brake pedal on said vehicle,

a first gear rotatable by said brake pedal,

a second gear meshingly engaging said first gear,

and a duality of crank arms simultaneously rotatable with said secondgear,

said crank arms being operatively connected with said pistons forimparting rectilinear movement to said pistons upon rotation of saidcrank arms to drive said pistons through said strokes, said crank armsbeing positioned such that the crank arm connected to the piston forsaid first cylinder imparts rectilinear movement thereto at anaccelerating rate with respect to the rectilinear movement imparted tosaid piston in said second cylinder, said first gear having a largerpitch circle than that of said second gear for thereby causing saidcrank arms to rotate through a greater are than said brake pedal.

5. A device as recited in claim 4 in which for causing said acceleratingrectilinear movement of said piston in said first cylinder the crank armoperatively connected thereto is arranged upon said rotation thereof toapproach an imaginary line normal to an extension of the axis of saidcylinders, and said crank arm for said piston in said second cylinderupon said rotation thereof is arranged to move away from said imaginaryline.

6. Incombination with a vehicle having hydraulic brakes at the frontwheels thereof and at the rear wheels thereof, a braking systemcomprising a duality of hydraulic systems, each of said systemsincluding a master hydraulic cylinder,

the first of said systems being operatively connected to said brakes atthe front wheels,

the second of said systems being operatively connected to said brakes atthe front wheels,

a piston in each of said cylinders for forcing fluid therefrom in thesystem thereof in a pressure stroke of such piston from a retracted toan extended position,

a brake pedal,

means rotatably mounting said brake pedal on said vehicle,

means interconnecting said brake pedal and said pistons for translatingrotation of said brake pedal into rectilinear movement of said pistonsthrough said strokes,

said translating means including a cam means for controlling the ratesof movement of said pistons,

and causing said piston in said first cylinder to accelerate relative tosaid piston in said second cylinder during at least a substantialportion of said strokes of said pistons,

and means for interconnecting said systems during initial portions ofsaid pressure strokes substantially until the time of application of thebrakes at said front wheels and at said rear wheels and for separat ingsaid systems following such application of said brakes.

7. In combination with a vehicle having front hydraulic brakes and rearhydraulic brakes, a braking system comprising a duality of hydraulicmaster cylinders mounted on said vehicle with their axes parallel,

the first of said cylinders having an outlet connected to said frontbrakes,

the second of said cylinders having an outlet connected to said rearbrakes,

a piston in each of said cylinders movable through a stroke toward saidoutlet from a retracted position to an extended position,

a brake pedal,

means rotatably mounting said brake pedal on said vehicle,

a first gear rotatable by and simultaneously with said brake pedal,

a second gear meshingly engaging said first gear and rotatable thereby,

means mounting said second gear on said vehicle for rotation of saidsecond gear about an axis,

said second gear having a pitch radius shorter than the pitch radius ofsaid first gear,

whereby said second gear rotates through a greater are than said firstgear upon rotation of said brake pedal,

a duality of crank arms rotatable by and simultaneously with said secondgear about said axis of said second gear,

the first of said crank arms being operatively connected to the pistonof said first cylinder,

the second of said crank arms being operatively connected to the pistonof said second cylinder for imparting rectilinear movement to saidpistons upon rotation of said crank arms,

said first crank arm being positioned to approach an imaginary linenormal to a projection of the axes of said cylinders,

and said second crank arm being positioned to move away from saidimaginary line upon said rotation of said crank arms,

8. In combination with a vehicle having front hydraulic brakes and rearhydraulic brakes, a braking system comprising a duality of hydraulicmaster cylinders mounted on said vehicle with their axes parallel,

the first of said cylinders having an outlet connected to said frontbrakes,

the second of said cylinders having an outlet connected to said rearbrakes,

a piston in each of said cylinders movable through a stroke toward saidoutlet from a retracted position to an extended position,

a brake pedal,

means rotatably mounting said brake pedal on said vehicle,

a duality of cams,

means rotatably mounting said cams on said vehicle,

the first of said cams engaging the piston in said first cylinder formoving said piston in said first cylinder through said stroke,

the second of said cams engaging the piston in said second cylinder formoving said piston in said second cylinder through said stroke,

and means interconnecting said brake pedal and said cams for rotatingsaid cams simultaneously with said brake pedal,

said cams being contoured to move said piston in said first cylinder atan accelerated rate with respect to said piston in said second cylinderduring at least the latter portions of said strokes of said pistons.

9. In combination with a vehicle having hydraulic brakes at the frontWheels thereof and at the rear wheels thereof, a braking systemcomprising a duality of axially parallel master hydraulic cylinders,

the first of said cylinders being operatively connected to said brakesat the front wheels,

the second of said cylinders being operatively connected to said brakesat the rear wheels,

a piston in each of said cylinders for forcing fluid therefrom in apressure stroke from a retracted to an extended position,

a brake pedal,

means rotatably mounting said brake pedal on said vehicle,

a duality of crank arms rotatable by said brake pedal,

means operatively connecting said crank arms with said pistons in saidcylinders for imparting movement to said pistons to drive said pistonsthrough said strokes upon rotation of said crank arms by said brakepedal,

said crank arms being positioned with respect to an imaginary linenormal to an extension of the axes of said cylinders such that upon suchrotation of said crank arms the crank arm operatively connected to saidpiston in said first cylinder approaches said line,

and said crank arm operatively connected to said piston in said secondcylinder moves away from said line.

10. A device as recited in claim 9 including in addition means forcausing said crank arms to rotate through greater arcs than the arc ofrotation of said brake pedal upon actuation of said brake pedal.

11. A device as recited in claim 9 including a passagewayinterconnecting said cylinders,

said passageway communicating with the circumferential wall of saidsecond cylinder a predetermined axial distance from the piston thereinwhen said last-mentioned piston is in said retracted position.

12. A device as recited in claim 9 including a bypass interconnectingsaid outlets of said cylinders,

and a pressure responsive valve means in said bypass for closing saidbypass upon generation of substantial back pressure from both said frontbrakes and said rear brakes.

13. A device as recited in claim 12 in which said valve means includes achamber series-connected in said bypass,

a valve member in said chamber,

a valve seat in said chamber engageable by said valve member for closingsaid valve,

a third cylinder communicating with said chamber,

a third piston in said third cylinder,

means interconnecting said valve member and said piston whereby saidpiston in response to fluid pres sure in said third cylinder from saidchamber urges said valve member toward said valve seat for closing saidbypass,

and resilient means biasing said piston to a position where said pistonholds said valve member in a spaced relationship with said valve seatfor opening said bypass.

I4. In combination with a vehicle having front wheels and rear wheels, abraking arrangement for said vehicle comprising fluid-operable frontwheel brakes,

fluid-operable rear wheel brakes,

a first hydraulic system for said front wheel brakes,

a second hydraulic system for said rear wheel brakes,

said first and second hydraulic systems including deformable componentshaving individual degrees of stiffness,

said first hydraulic system including a first master cylinder and afirst piston therein movable through a stroke for delivering fluid insaid first hydraulic system to said front wheel brakes,

said second hydraulic system including a second master cylinder and asecond piston therein movable through a stroke for delivering fluid insaid second hydraulic system to said rear wheel brakes,

manually movable means for providing a brake-applying force,

and means for transmitting said force to said first and said secondpistons for moving said first and said second pistons and deliveringfluid to said front and rear wheel brakes for thereby applying saidfront wheel brakes and said rear wheel brakes,

said force transmitting means including means for delivering fluid tosaid front and rear brakes in amounts sufiicient to deform saiddeformable components and produce a predetermined ratio of braking forceat said front wheels to said braking force at said rear wheels in whichsaid braking force at said front wheels is greater than said brakingforce at said rear wheels during a substantial portion of the movementof said pistons, and said force transmitting means including means forincreasing said braking force at said front wheels at an acceleratedrate relative to said braking force at said rear wheels.

15. In combination with a vehicle having front and rear wheels, abraking device comprising a front hydraulic brake system including frontbrakes at said front wheels,

a rear hydraulic brake system including rear brakes at said rear wheels,

said front and rear hydraulic brake systems having elasticcharacteristics,

a braking arrangement for said said second cam means being operativelycon-.

nected to said rear brake system for applying said rear brakes uponmovement of said second cam means,

said first and second cam means including means for applying said frontbrakes at an increasing rate of increase and said rear brakes at acomplementarily decreasing rate of increase upon increasing movement ofsaid pedal for compensating for the increase in effective weight at saidfront wheels and the decrease in effective weight at said rear wheelsupon deceleration of said vehicle, said first and second cam meansincluding means for producing ranges of movement sufficient tocompensate for said elastic characteristics of said front hydraulicbrake system and of said rear hydraulic brake system in so applying saidfront and rear brakes. 16. In combination with a vehicle lhaving frontwheels,

vehicle comprising front brakes at said front wheels, rear brakes atsaid rear wheels, means for producing an operating force, means fortransmitting a first portion of said force to said front wheels and asecond portion of said force to said rear wheels, hydraulic means atsaid front wheels for receiving said first portion of said force forapplying the same to said front brakes for producing a stopping force,hydraulic means at said rear wheels for receiving said second portion ofsaid force for applying the same to said rear brakes for producing astopping force,

both of said hydraulic means having elastic characteristics, and meansfor varying said first portion relative to said second portion forproviding an increasing ration of said first portion of said force tosaid second portion of said force upon an increase in said operatingforce so as to produce an increase in the application of the portion ofsaid operating force to said front wheels relative to the application ofsaid operating force to said rear wheels to obtain substantially maximumdeclerating forces at said wheels at various coefficients of friction ofsaid front and rear wheels relative to a supporting surface, said meansfor varying said first portion relative to said second portion includingmeans for varying said first portion to said second portion inaccordance with said elastic characteristics of said hydraulic means atsaid front wheels and said hydraulic means at said rear wheels,

17. In combination with a vehicle having front wheels and rear wheels, abraking arangement f r said vehicle comprising front brakes at saidfront wheels, rear brakes at said rear wheels, actuator means movablefor producing an operating force, means for transmitting a first portionof said force to said front wheels and a second portion of said force tosaid rear wheels, hydraulic means at said front wheels for receivingsaid first portion of said force for applying the same to said frontbrakes for producing a firststopping force, hydraulic means at said rearwheels for receiving said second portion of said force for applying thesame to said rear brakes for producing a second stopping force,

both of said hydraulic means having elastic clharacteristics, and meansfor predeterminately varying said first portion and said second portionrelative to each other upon increasing movement of said actuator means,said means for predeterminately varying said first portion and saidsecond portion relative to each other including means for providing anincreasing ratio of said first stopping force to said second stoppingforce upon increasing movement of said actuator means in an amountsufficient to compensate for said elastic characteristics of saidhydraulic means at said front wheels and said hydraulic means at saidrear wheels, said means for predeterminately varying said first portionand said second portion relative to each other further including meansfor producing a relationship of the ratio of said first stopping forceto said second stopping force relative to the total stoppin forceproduced by the sum of the said first stopping force and said secondstopping force such that when said ratio is plotted as the ordinate andsaid total stopping force is plotted as the abscissa a curve is producedthat inclines upwardly to the right and is concave upwardly,

for thereby obtaining substantially maximum deceleration forces at saidwheels at various coeflicients of friction of said front and rear wheelsrelative to a supporting surface.

References Cited The following references, cited by the Examiner, are

of record in the patented file of this patent or the original MILTONBUCHLER, Primary Examiner I. I MCLAUGHIN, JR., Assistant Examiner US.Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Reissue No. 26,643August 12, 1969 Harvison C. Holland It is certified that error appearsin the above identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 44 after [leakage]" insert linkage Column 12, line 18,att he" should read at the line 20, "front" should read rear Column 15,line 50, "ration" should read ratio Column 16, line 13, firststoppingshould read first stopping Signed and sealed this 28th day of April1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Atteating Officer Commissioner of Patents

